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1
Delta Island AgricultureDelta Island Agriculture
Technical Workshop onModeling Issues of the Delta
February 6, 2007
Jim Wilde, P.E.Delta Modeling SectionCalifornia Department of Water Resources
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Discussion TopicsDiscussion Topics
• Delta Island Consumptive Use (DICU)– Model description
• DICU model results– How does the model do?
• DICU uncertainties– What are the inherent model uncertainties
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DICU Model InputsDICU Model Inputs
• 142 subareasSome islands contain > 1 subarea
• 20 land use typesEach type is aggregated for each subarea
• 7 precipitation stationsDistributed by Thiessen Polygon method
• Constant seepage into low lands0.3 inches per foot of crop root depth per month
• Long term average crop consumptive useCU is then adjusted by pan evaporation
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DICU Model OutputsDICU Model Outputs
• Diversions– Water taken out of channels
• Seepage– Channel loss to the islands
• Drains– Return water pumped back
to channels
Monthly Average:Monthly Average:
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Ag Diversions and DrainsAg Diversions and Drains
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Impact of Ag Use in Dry PeriodsImpact of Ag Use in Dry Periods
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DICU Model UncertaintyDICU Model Uncertainty
• Irrigation– Fixed seasons for each crop– Schedule differs for critical and non-critical water year
types
• Monthly time step reduces variability– Stormwater runoff cannot be estimated
• Long term historic land use patterns not used– The land use is assumed constant– Double cropping not considered
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DICU Model UncertaintyDICU Model Uncertainty
• Leaching patterns are assumed the same every year– Applied as a post-processing step
• CU adjustment from one pan evaporation location– Uncertainty in spatial variability
• What are the farmers really doing?– Estimating local water management practices
can be challenging at best
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Now on to Delta AG Water Quality Now on to Delta AG Water Quality